<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    class Cat {
      sayThis() {
        console.log(this); // 这里的 `this` 指向谁？undefined
      }

      exec(cb) {
        cb();
      }

      render() {
        this.exec(this.sayThis);
      }
    }
    const cat = new Cat();
    cat.render(); // 输出结果是什么？
  </script>
</body>

</html>